< draft-ietf-msdp-spec-15.txt		draft-ietf-msdp-spec-16.txt >
	Network Working Group David Meyer
	(Editor)
	INTERNET DRAFT Bill Fenner
	(Editor)
	Category
	Standards Track
	April, 2003		INTERNET-DRAFT Bill Fenner (Editor)
			draft-ietf-msdp-spec-16.txt David Meyer (Editor)
			Category Informational
			Expires: November 2003 May 2003
	Multicast Source Discovery Protocol (MSDP)		Multicast Source Discovery Protocol (MSDP)
	<draft-ietf-msdp-spec-15.txt>		<draft-ietf-msdp-spec-16.txt>
	Status of this Memo		Status of this Document
	This document is an Internet-Draft and is in full conformance with		This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC 2026.		all provisions of Section 10 of RFC2026.
	Internet Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that other		Task Force (IETF), its areas, and its working groups. Note that
	groups may also distribute working documents as Internet-Drafts.		other groups may also distribute working documents as Internet-
			Drafts.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
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	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
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	http://www.ietf.org/ietf/1id-abstracts.txt.		http://www.ietf.org/ietf/1id-abstracts.txt
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	Abstract		This document is a product of an individual. Comments are solicited
			and should be addressed to the author(s).
			Copyright Notice
			Copyright (C) The Internet Society (2003). All Rights Reserved.
			Abstract
	The Multicast Source Discovery Protocol, MSDP, describes a mechanism		The Multicast Source Discovery Protocol, MSDP, describes a mechanism
	to connect multiple PIM-SM domains together. Each PIM-SM domain uses		to connect multiple IP Version 4 Protocol Independent Multicast
	its own independent Rendezvous Point (RP) and does not have to depend		Sparse-Mode (PIM-SM) [RFC2362] domains together. Each PIM-SM domain
	on RPs in other domains. This draft is intended to document existing		uses its own independent Rendezvous Point (RP) and does not have to
	MSDP implementations in the field.		depend on RPs in other domains. This draft is intended to document
			existing MSDP implementations in the field.
	Copyright Notice		Table of Contents
	Copyright (C) The Internet Society (2003). All Rights Reserved.		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
			2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
			3. Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . 5
			4. Caching. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
			5. Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
			5.1. SA-Advertisement-Timer. . . . . . . . . . . . . . . . . . . 7
			5.2. SA-Advertisement-Timer Processing . . . . . . . . . . . . . 8
			5.3. SA Cache Timeout (SA-State Timer) . . . . . . . . . . . . . 8
			5.4. Peer Hold Timer . . . . . . . . . . . . . . . . . . . . . . 8
			5.5. KeepAlive Timer . . . . . . . . . . . . . . . . . . . . . . 9
			5.6. ConnectRetry Timer. . . . . . . . . . . . . . . . . . . . . 9
			6. Intermediate MSDP Peers. . . . . . . . . . . . . . . . . . . . 9
			7. SA Filtering and Policy. . . . . . . . . . . . . . . . . . . . 10
			8. Encapsulated Data Packets. . . . . . . . . . . . . . . . . . . 10
			9. Other Scenarios. . . . . . . . . . . . . . . . . . . . . . . . 10
			10. MSDP Peer-RPF Forwarding. . . . . . . . . . . . . . . . . . . 11
			10.1. Definitions. . . . . . . . . . . . . . . . . . . . . . . . 11
			10.1.1. Multicast RPF Routing Information Base (MRIB). .. . . . 11
			10.1.2. Peer-RPF Route. . . . . . . . . . . . . . . . . . . . . 11
			10.1.3. Peer-RPF Forwarding Rules . . . . . . . . . . . . . . . 11
			10.2. MSDP mesh-group semantics. . . . . . . . . . . . . . . . . 13
			11. MSDP Connection State Machine . . . . . . . . . . . . . . . . 14
			11.1. Events . . . . . . . . . . . . . . . . . . . . . . . . . . 15
			11.2. Actions. . . . . . . . . . . . . . . . . . . . . . . . . . 16
			11.3. Peer-specific Events . . . . . . . . . . . . . . . . . . . 16
			11.4. Peer-independent Events. . . . . . . . . . . . . . . . . . 17
			12. Packet Formats. . . . . . . . . . . . . . . . . . . . . . . . 17
			12.1. MSDP TLV format. . . . . . . . . . . . . . . . . . . . . . 17
			12.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 18
			12.2.1. IPv4 Source-Active TLV. . . . . . . . . . . . . . . . . 18
			12.2.2. KeepAlive TLV . . . . . . . . . . . . . . . . . . . . . 20
			13. MSDP Error Handling . . . . . . . . . . . . . . . . . . . . . 20
			14. SA Data Encapsulation . . . . . . . . . . . . . . . . . . . . 21
			15. Applicability Statement . . . . . . . . . . . . . . . . . . . 21
			15.1. Between PIM Domains. . . . . . . . . . . . . . . . . . . . 21
			15.2. Between Anycast-RPs. . . . . . . . . . . . . . . . . . . . 21
			16. Intellectual Property . . . . . . . . . . . . . . . . . . . . 21
			17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
			18. Security Considerations . . . . . . . . . . . . . . . . . . . 23
			19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
			20. References. . . . . . . . . . . . . . . . . . . . . . . . . . 24
			20.1. Normative References . . . . . . . . . . . . . . . . . . . 24
			20.2. Informative References . . . . . . . . . . . . . . . . . . 25
			21. Editor's Addresses. . . . . . . . . . . . . . . . . . . . . . 25
			22. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 25
	1. Introduction		1. Introduction
	The Multicast Source Discovery Protocol, MSDP, describes a mechanism		The Multicast Source Discovery Protocol, MSDP, describes a mechanism
	to connect multiple PIM-SM domains together. Each PIM-SM domain uses		to connect multiple PIM Sparse-Mode (PIM-SM) [RFC2362] domains
	its own independent RP(s) and does not have to depend on RPs in other		together. Each PIM-SM domain uses its own independent RP(s) and does
	domains. Advantages of this approach include:		not have to depend on RPs in other domains. Advantages of this
			approach include:
	o No Third-party resource dependencies on RP		o No Third-party resource dependencies on a domain's RP
	PIM-SM domains can rely on their own RPs only.		PIM-SM domains can rely on their own RPs only.
	o Receiver only Domains		o Receiver only Domains
	Domains with only receivers get data without globally		Domains with only receivers get data without globally
	advertising group membership.		advertising group membership.
	Note that MSDP may be used with protocols other than PIM-SM, but such		Note that MSDP may be used with protocols other than PIM-SM, but such
	usage is not specified in this memo.		usage is not specified in this memo.
	The keywords MUST, MUST NOT, MAY, OPTIONAL, REQUIRED, RECOMMENDED,		2. Overview
	SHALL, SHALL NOT, SHOULD, SHOULD NOT are to be interpreted as defined
	in RFC 2119 [RFC2119].
	2. Overview
	MSDP-speaking routers in a PIM-SM [RFC2362] domain have a MSDP		MSDP-speaking routers in a PIM-SM domain have a MSDP peering
	peering relationship with MSDP peers in another domain. The peering		relationship with MSDP peers in another domain. The peering
	relationship is made up of a TCP connection in which control		relationship is made up of a TCP connection in which control
	information is exchanged. Each domain has one or more connections to		information is exchanged. Each domain has one or more connections to
	this virtual topology.		this virtual topology.
	The purpose of this topology is to allow domains to discover		The purpose of this topology is to allow domains to discover
	multicast sources from other domains. If the multicast sources are of		multicast sources from other domains. If the multicast sources are of
	interest to a domain which has receivers, the normal source-tree		interest to a domain which has receivers, the normal source-tree
	building mechanism in PIM-SM will be used to deliver multicast data		building mechanism in PIM-SM will be used to deliver multicast data
	over an inter-domain distribution tree.		over an inter-domain distribution tree.
	3. Procedure		3. Procedure
	When an RP in a PIM-SM domain first learns of a new sender, e.g. via		When an RP in a PIM-SM domain first learns of a new sender, e.g. via
	PIM register messages, it constructs a "Source-Active" (SA) message		PIM register messages, it constructs a "Source-Active" (SA) message
	and sends it to its MSDP peers. All RPs, which intend to originate		and sends it to its MSDP peers. All RPs, which intend to originate or
	or receive SA messages, must establish MSDP peering with other RPs,		receive SA messages, must establish MSDP peering with other RPs,
	either directly or via an intermediate MSDP peer. The SA message		either directly or via an intermediate MSDP peer. The SA message
	contains the following fields:		contains the following fields:
	o Source address of the data source.		o Source address of the data source.
	o Group address the data source sends to.
	o IP address of the RP.		o Group address the data source sends to.
			o IP address of the RP.
	Note that an RP that isn't a DR on a shared network SHOULD NOT		Note that an RP that isn't a DR on a shared network SHOULD NOT
	originate SA's for directly connected sources on that shared network;		originate SA's for directly connected sources on that shared network;
	it should only originate in response to receiving Register messages		it should only originate in response to receiving Register messages
	from the DR.		from the DR.
	Each MSDP peer receives and forwards the message away from the RP		Each MSDP peer receives and forwards the message away from the RP
	address in a "peer-RPF flooding" fashion. The notion of peer-RPF		address in a "peer-RPF flooding" fashion. The notion of peer-RPF
	flooding is with respect to forwarding SA messages. The Multicast RPF		flooding is with respect to forwarding SA messages. The Multicast RPF
	Routing Information Base (MRIB) is examined to determine which peer		Routing Information Base (MRIB) is examined to determine which peer
	skipping to change at line 115 ¶		skipping to change at page 6, line 34 ¶
	is called an "RPF peer". See section 13 for the details of peer-RPF		is called an "RPF peer". See section 13 for the details of peer-RPF
	forwarding.		forwarding.
	If the MSDP peer receives the SA from a non-RPF peer towards the		If the MSDP peer receives the SA from a non-RPF peer towards the
	originating RP, it will drop the message. Otherwise, it forwards the		originating RP, it will drop the message. Otherwise, it forwards the
	message to all its MSDP peers (except the one from which it received		message to all its MSDP peers (except the one from which it received
	the SA message).		the SA message).
	When an MSDP peer which is also an RP for its own domain receives a		When an MSDP peer which is also an RP for its own domain receives a
	new SA message, it determines if there are any group members within		new SA message, it determines if there are any group members within
	the domain interested in any group described by an (S,G) entry within		the domain interested in any group described by an (Source, Group),
	the SA message. That is, the RP checks for a (*,G) entry with a non-		or (S,G) entry within the SA message. That is, the RP checks for a
	empty outgoing interface list; this implies that some system in the		(*,G) entry with a non-empty outgoing interface list; this implies
	domain is interested in the group. In this case, the RP triggers a		that some system in the domain is interested in the group. In this
	(S,G) join event towards the data source as if a Join/Prune message		case, the RP triggers a (S,G) join event towards the data source as
	was received addressed to the RP itself. This sets up a branch of the		if a Join/Prune message was received addressed to the RP itself. This
	source-tree to this domain. Subsequent data packets arrive at the RP		sets up a branch of the source-tree to this domain. Subsequent data
	via this tree branch, and are forwarded down the shared-tree inside		packets arrive at the RP via this tree branch, and are forwarded down
	the domain. If leaf routers choose to join the source-tree they have		the shared-tree inside the domain. If leaf routers choose to join the
	the option to do so according to existing PIM-SM conventions.		source-tree they have the option to do so according to existing PIM-
	Finally, if an RP in a domain receives a PIM Join message for a new		SM conventions. Finally, if an RP in a domain receives a PIM Join
	group G, the RP SHOULD trigger a (S,G) join event for each active		message for a new group G, the RP SHOULD trigger a (S,G) join event
	(S,G) for that group in its SA cache.		for each active (S,G) for that group in its SA cache.
	This procedure has been affectionately named flood-and-join because		This procedure has been affectionately named flood-and-join because
	if any RP is not interested in the group, they can ignore the SA		if any RP is not interested in the group, they can ignore the SA
	message. Otherwise, they join a distribution tree.		message. Otherwise, they join a distribution tree.
	4. Caching		4. Caching
	A MSDP speaker MUST cache SA messages. Caching allows pacing of MSDP		A MSDP speaker MUST cache SA messages. Caching allows pacing of MSDP
	messages as well as reducing join latency for new receivers of a		messages as well as reducing join latency for new receivers of a
	group G at an originating RP which has existing MSDP (S,G) state. In		group G at an originating RP which has existing MSDP (S,G) state. In
	addition, caching greatly aids in diagnosis and debugging of various		addition, caching greatly aids in diagnosis and debugging of various
	problems.		problems.
	An MSDP speaker must provide a mechanism to reduce the forwarding of		An MSDP speaker must provide a mechanism to reduce the forwarding of
	new SA's. The SA-cache is used to reduce storms and performs this		new SA's. The SA-cache is used to reduce storms and performs this by
	by not forwarding SA's unless they are in the cache or are new SA		not forwarding SA's unless they are in the cache or are new SA
	packets that the MSDP speaker will cache for the first time. The		packets that the MSDP speaker will cache for the first time. The SA-
	SA-cache also reduces storms by advertising from the cache at a		cache also reduces storms by advertising from the cache at a period
	period of no more than twice per SA-Advertisement-Timer interval and		of no more than twice per SA-Advertisement-Timer interval and not
	not less than 1 time per SA Advertisment period.		less than 1 time per SA Advertisement period.
	5. Timers		5. Timers
	The main timers for MSDP are: SA-Advertisement-Timer, SA Cache Entry		The main timers for MSDP are: SA-Advertisement-Timer, SA Cache Entry
	timer, Peer Hold Timer, KeepAlive timer, and ConnectRetry timer.		timer, Peer Hold Timer, KeepAlive timer, and ConnectRetry timer. Each
	Each is considered below.		is considered below.
	5.1. SA-Advertisement-Timer		5.1. SA-Advertisement-Timer
	RPs which originate SA messages do so periodically as long as there		RPs which originate SA messages do so periodically as long as there
	is data being sent by the source. There is one SA-Advertisement-Timer		is data being sent by the source. There is one SA-Advertisement-Timer
	covering the sources that an RP may advertise. [SA-Advertisement-		covering the sources that an RP may advertise. [SA-Advertisement-
	Period] MUST be 60 seconds. An RP MUST not send more than one		Period] MUST be 60 seconds. An RP MUST not send more than one
	periodic SA message for a given (S,G) within an SA Advertisement		periodic SA message for a given (S,G) within an SA Advertisement
	interval. Originating periodic SA messages is required to keep		interval. Originating periodic SA messages is required to keep
	announcements alive in caches. Finally, an originating RP SHOULD		announcements alive in caches. Finally, an originating RP SHOULD
	trigger the transmission of an SA message as soon as it receives data		trigger the transmission of an SA message as soon as it receives data
	from an internal source for the first time. This initial SA message		from an internal source for the first time. This initial SA message
	may be in addition to the periodic sa-message forwarded in that first		may be in addition to the periodic sa-message forwarded in that first
	60 seconds for that S,G.		60 seconds for that (S,G).
	5.2. SA-Advertisement-Timer Processing		5.2. SA-Advertisement-Timer Processing
	An RP MUST spread the generation of periodic SA messages (i.e.		An RP MUST spread the generation of periodic SA messages (i.e.
	messages advertising the active sources for which it is the RP) over		messages advertising the active sources for which it is the RP) over
	its reporting interval (i.e. SA-Advertisement-Period). An RP starts		its reporting interval (i.e. SA-Advertisement-Period). An RP starts
	the SA-Advertisement-Timer when the MSDP process is configured. When		the SA-Advertisement-Timer when the MSDP process is configured. When
	the timer expires, an RP resets the timer to [SA-Advertisement-		the timer expires, an RP resets the timer to [SA-Advertisement-
	Period] seconds, and begins the advertisement of its active sources.		Period] seconds, and begins the advertisement of its active sources.
	Active sources are advertised in the following manner: An RP packs		Active sources are advertised in the following manner: An RP packs
	its active sources into an SA message until the largest MSDP packet		its active sources into an SA message until the largest MSDP packet
	that can be sent is built or there are no more sources, and then		that can be sent is built or there are no more sources, and then
	sends the message. This process is repeated periodically within the		sends the message. This process is repeated periodically within the
	SA-Advertisement-Period in such a way that all of the RP's sources		SA-Advertisement-Period in such a way that all of the RP's sources
	are advertised. Note that since MSDP is a periodic protocol, an		are advertised. Note that since MSDP is a periodic protocol, an
	implemenation SHOULD send all cached SA messages when a connection is		implementation SHOULD send all cached SA messages when a connection
	established. Finally, the timer is deleted when the MSDP process is		is established. Finally, the timer is deleted when the MSDP process
	deconfigured.		is de-configured.
	5.3. SA Cache Timeout (SA-State Timer)		5.3. SA Cache Timeout (SA-State Timer)
	Each entry in an SA Cache has an associated SA-State Timer. A		Each entry in an SA Cache has an associated SA-State Timer. A
	(S,G)-SA-State-Timer is started when an (S,G)-SA message is initially		(S,G)-SA-State-Timer is started when an (S,G)-SA message is initially
	received by an MSDP peer. The timer is reset to [SG-State-Period] if		received by an MSDP peer. The timer is reset to [SG-State-Period] if
	another (S,G)-SA message is received before the (S,G)-SA-State Timer		another (S,G)-SA message is received before the (S,G)-SA-State Timer
	expires. [SG-State-Period] MUST NOT be less than		expires. [SG-State-Period] MUST NOT be less than [SA-Advertisement-
	[SA-Advertisement-Period] + [SA-Hold-Down-Period].		Period] + [SA-Hold-Down-Period].
	5.4. Peer Hold Timer		5.4. Peer Hold Timer
	The Hold Timer is initialized to [HoldTime-Period] when the peer's		The Hold Timer is initialized to [HoldTime-Period] when the peer's
	transport connection is established, and is reset to [HoldTime-		transport connection is established, and is reset to [HoldTime-
	Period] when any MSDP message is received. Finally, the timer is		Period] when any MSDP message is received. Finally, the timer is
	deleted when the peer's transport connection is closed.		deleted when the peer's transport connection is closed. [HoldTime-
	[HoldTime-Period] MUST be at least three seconds. The recommended		Period] MUST be at least three seconds. The recommended value for
	value for [HoldTime-Period] is 75 seconds.		[HoldTime-Period] is 75 seconds.
	5.5. KeepAlive Timer		5.5. KeepAlive Timer
	Once an MSDP transport connection is established, each side of the		Once an MSDP transport connection is established, each side of the
	connection sends a KeepAlive message and sets a KeepAlive timer. If		connection sends a KeepAlive message and sets a KeepAlive timer. If
	the KeepAlive timer expires, the local system sends a KeepAlive		the KeepAlive timer expires, the local system sends a KeepAlive
	message and restarts its KeepAlive timer.		message and restarts its KeepAlive timer.
	The KeepAlive timer is set to [KeepAlive-Period] when the peer comes		The KeepAlive timer is set to [KeepAlive-Period] when the peer comes
	up. The timer is reset to [KeepAlive-Period] each time an MSDP		up. The timer is reset to [KeepAlive-Period] each time an MSDP
	message is sent to the peer, and reset when the timer expires.		message is sent to the peer, and reset when the timer expires.
	Finally, the KeepAlive timer is deleted when the peer's transport		Finally, the KeepAlive timer is deleted when the peer's transport
	connection is closed.		connection is closed.
	[KeepAlive-Period] MUST be less than [HoldTime-Period], and MUST be		[KeepAlive-Period] MUST be less than [HoldTime-Period], and MUST be
	at least one second. The recommended value for [KeepAlive-Period] is		at least one second. The recommended value for [KeepAlive-Period] is
	60 seconds.		60 seconds.
	5.6. ConnectRetry Timer		5.6. ConnectRetry Timer
	The ConnectRetry timer is used by the MSDP peer with the lower IP		The ConnectRetry timer is used by the MSDP peer with the lower IP
	address to transition from INACTIVE to CONNECTING states. There is		address to transition from INACTIVE to CONNECTING states. There is
	one timer per peer, and the [ConnectRetry-Period] SHOULD be set to 30		one timer per peer, and the [ConnectRetry-Period] SHOULD be set to 30
	seconds. The timer is initialized to [ConnectRetry-Period] when an		seconds. The timer is initialized to [ConnectRetry-Period] when an
	MSDP speaker attempts to actively open a TCP connection to its peer		MSDP speaker attempts to actively open a TCP connection to its peer
	(see section 15, event E2, action A2 ). When the timer expires, the		(see section 15, event E2, action A2 ). When the timer expires, the
	peer retries the connection and the timer is reset to [ConnectRetry-		peer retries the connection and the timer is reset to [ConnectRetry-
	Period]. It is deleted if either the connection transitions into		Period]. It is deleted if either the connection transitions into
	ESTABLISHED state or the peer is deconfigured.		ESTABLISHED state or the peer is de-configured.
	6. Intermediate MSDP Peers		6. Intermediate MSDP Peers
	Intermediate MSDP speakers do not originate periodic SA messages on		Intermediate MSDP speakers do not originate periodic SA messages on
	behalf of sources in other domains. In general, an RP MUST only		behalf of sources in other domains. In general, an RP MUST only
	originate an SA for a source which would register to it, and ONLY RPs		originate an SA for a source which would register to it, and ONLY RPs
	may originate SA messages.		may originate SA messages.
	7. SA Filtering and Policy		7. SA Filtering and Policy
	As the number of (S,G) pairs increases in the Internet, an RP may		As the number of (S,G) pairs increases in the Internet, an RP may
	want to filter which sources it describes in SA messages. Also,		want to filter which sources it describes in SA messages. Also,
	filtering may be used as a matter of policy which at the same time		filtering may be used as a matter of policy which at the same time
	can reduce state. MSDP peers in transit domains should not filter		can reduce state. MSDP peers in transit domains should not filter SA
	SA messages or the flood-and-join model can not guarantee that		messages or the flood-and-join model can not guarantee that sources
	sources will be known throughout the Internet (i.e., SA filtering		will be known throughout the Internet (i.e., SA filtering by transit
	by transit domains may cause undesired lack of connectivity). In		domains may cause undesired lack of connectivity). In general, policy
	general, policy should be expressed using MBGP [RFC2283]. This		should be expressed using MBGP [RFC2283]. This will cause MSDP
	will cause MSDP messages to flow in the desired direction and		messages to flow in the desired direction and peer-RPF fail
	peer-RPF fail otherwise. An exception occurs at an administrative		otherwise. An exception occurs at an administrative scope [RFC2365]
	scope [RFC2365] boundary. In particular, a SA message for a (S,G)		boundary. In particular, a SA message for a (S,G) MUST NOT be sent to
	MUST NOT be sent to peers which are on the other side of an		peers which are on the other side of an administrative scope boundary
	administrative scope boundary for G.		for G.
	8. Encapsulated Data Packets		8. Encapsulated Data Packets
	The RP MAY encapsulate multicast data from the source. An interested		The RP MAY encapsulate multicast data from the source. An interested
	RP may decapsulate the packet, which SHOULD be forwarded as if a PIM		RP may decapsulate the packet, which SHOULD be forwarded as if a PIM
	register encapsulated packet was received. That is, if packets are		register encapsulated packet was received. That is, if packets are
	already arriving over the interface toward the source, then the		already arriving over the interface toward the source, then the
	packet is dropped. Otherwise, if the outgoing interface list is non-		packet is dropped. Otherwise, if the outgoing interface list is non-
	null, the packet is forwarded appropriately. Note that when doing		null, the packet is forwarded appropriately. Note that when doing
	data encapsulation, an implementation MUST bound the time during		data encapsulation, an implementation MUST bound the time during
	which packets are encapsulated.		which packets are encapsulated.
	This allows for small bursts to be received before the multicast tree		This allows for small bursts to be received before the multicast tree
	is built back toward the source's domain. For example, an		is built back toward the source's domain. For example, an
	implementation SHOULD encapsulate at least the first packet to		implementation SHOULD encapsulate at least the first packet to
	provide service to bursty sources.		provide service to bursty sources.
	9. Other Scenarios		9. Other Scenarios
	MSDP is not limited to deployment across different routing domains.		MSDP is not limited to deployment across different routing domains.
	It can be used within a routing domain when it is desired to deploy		It can be used within a routing domain when it is desired to deploy
	multiple RPs for the same group ranges such as with Anycast RP's.		multiple RPs for the same group ranges such as with Anycast RP's. As
	As long as all RPs have a interconnected MSDP topology, each can		long as all RPs have a interconnected MSDP topology, each can learn
	learn about active sources as well as RPs in other domains.		about active sources as well as RPs in other domains.
	10. MSDP Peer-RPF Forwarding		10. MSDP Peer-RPF Forwarding
	The MSDP Peer-RPF Forwarding rules are used for forwarding SA		The MSDP Peer-RPF Forwarding rules are used for forwarding SA
	messages throughout an MSDP enabled internet. Unlike the RPF check		messages throughout an MSDP enabled internet. Unlike the RPF check
	used when forwarding data packets, which generally compares the		used when forwarding data packets, which generally compares the
	packet's source address against the interface upon which the packet		packet's source address against the interface upon which the packet
	was received, the Peer-RPF check compares the RP address carried in		was received, the Peer-RPF check compares the RP address carried in
	the SA message against the MSDP peer from which the message was		the SA message against the MSDP peer from which the message was
	received.		received.
	10.1. Definitions		10.1. Definitions
	The following definitions are used in the description of the Peer-RPF		The following definitions are used in the description of the Peer-RPF
	Forwarding Rules:		Forwarding Rules:
	10.1.1. Multicast RPF Routing Information Base (MRIB)		10.1.1. Multicast RPF Routing Information Base (MRIB)
	The MRIB is the multicast topology table. It is typically derived		The MRIB is the multicast topology table. It is typically derived
	from the unicast routing table or from other routing protocols such		from the unicast routing table or from other routing protocols such
	as multi-protocol BGP [RFC2283].		as multi-protocol BGP [RFC2283].
	10.1.2. Peer-RPF Route		10.1.2. Peer-RPF Route
	The Peer-RPF route is the route that the MRIB chooses for a given		The Peer-RPF route is the route that the MRIB chooses for a given
	address. The Peer-RPF route for a SA's originating RP is used to		address. The Peer-RPF route for a SA's originating RP is used to
	select the peer from which the SA is accepted.		select the peer from which the SA is accepted.
	10.2. Peer-RPF Forwarding Rules		10.1.3. Peer-RPF Forwarding Rules
	An SA message originated by R and received by X from N is
	accepted if N is the peer-RPF neighbor for X, and is discarded
	otherwise.
	MPP(R,N) MP(N,X)		An SA message originated by R and received by X from N is accepted if
	R ---------....-------> N ------------------> X		N is the peer-RPF neighbor for X, and is discarded otherwise.
	SA(S,G,R) SA(S,G,R)
	MP(N,X) is an MSDP peering between N and X. MPP(R,N) is		MPP(R,N) MP(N,X)
	an MSDP peering path (zero or more MSDP peers) between		R ---------....-------> N ------------------> X
	R and N, e.g. MPP(R,N) = MP(R, A) + MP(A, B) + MP(B,		SA(S,G,R) SA(S,G,R)
	N). SA(S,G,R) is an SA message for source S on group G
	originated by an RP R.
	The peer-RPF neighbor N is chosen deterministically, using the		MP(N,X) is an MSDP peering between N and X. MPP(R,N) is an MSDP
	first of the following rules that matches. In particular,		peering path (zero or more MSDP peers) between R and N, e.g. MPP(R,N)
	N is the RPF neighbor of X with respect to R if		= MP(R, A) + MP(A, B) + MP(B, N). SA(S,G,R) is an SA message for
			source S on group G originated by an RP R.
	(i). N == R (X has an MSDP peering with R).		The peer-RPF neighbor N is chosen deterministically, using the first
			of the following rules that matches. In particular, N is the RPF
			neighbor of X with respect to R if
			(i). N == R (X has an MSDP peering with R).
	(ii). N is the eBGP NEXT_HOP of the Peer-RPF route		(ii). N is the eBGP NEXT_HOP of the Peer-RPF route for R.
	for R.
	(iii). The Peer-RPF route for R is learned through a		(iii). The Peer-RPF route for R is learned through a
	distance-vector or path-vector routing protocol		distance-vector or path-vector routing protocol
	(e.g. BGP, RIP, DVMRP) and N is the neighbor that		(e.g. BGP, RIP, DVMRP) and N is the neighbor that
	advertised the Peer-RPF route for R (e.g. N is the		advertised the Peer-RPF route for R (e.g. N is the iBGP
	iBGP advertiser of the route for R), or N is the		advertiser of the route for R), or N is the IGP next hop
	IGP next hop for R if the route for R is learned		for R if the route for R is learned via a link-state
	via a link-state protocol (e.g. OSPF or ISIS).		protocol (e.g. OSPF [RFC2178] or IS-IS [RFC1142]).
	(iv). N resides in the closest AS in the best path towards		(iv). N resides in the closest AS in the best path towards
	R. If multiple MSDP peers reside in the closest AS,		R. If multiple MSDP peers reside in the closest AS, the
	the peer with the highest IP address is the rpf-peer.		peer with the highest IP address is the rpf-peer.
	(v). N is configured as the static RPF-peer for R.		(v). N is configured as the static RPF-peer for R.
	MSDP peers, which are NOT in state ESTABLISHED (ie down peers), are		MSDP peers, which are NOT in state ESTABLISHED (i.e., down peers),
	not eligible for peer RPF consideration.		are not eligible for peer RPF consideration.
	10.3. MSDP mesh-group semantics		10.2. MSDP mesh-group semantics
	An MSDP mesh-group is a operational mechanism for reducing SA		An MSDP mesh-group is a operational mechanism for reducing SA
	flooding, typically in an intra-domain setting. In particular, when		flooding, typically in an intra-domain setting. In particular, when
	some subset of a domain's MSDP speakers are fully meshed, they can be		some subset of a domain's MSDP speakers are fully meshed, they can be
	configured into a mesh-group.		configured into a mesh-group.
	Note that mesh-groups assume that a member doesn't have to forward an		Note that mesh-groups assume that a member doesn't have to forward an
	SA to other members of the mesh-group because the originator will		SA to other members of the mesh-group because the originator will
	forward to all members. To be able for the originator to forward to		forward to all members. To be able for the originator to forward to
	all members (and to have each member also be a potential originator),		all members (and to have each member also be a potential originator),
	the mesh-group must be a full mesh of MSDP peering among all members.		the mesh-group must be a full mesh of MSDP peering among all members.
	The semantics of the mesh-group are as follows:		The semantics of the mesh-group are as follows:
	(i). If a member R of a mesh-group M receives a SA message from an		(i). If a member R of a mesh-group M receives a SA message
	MSDP peer that is also a member of mesh-group M, R accepts the		from an MSDP peer that is also a member of mesh-group M,
	SA message and forwards it to all of its peers that are not		R accepts the SA message and forwards it to all of its
	part of mesh-group M. R MUST NOT forward the SA message to		peers that are not part of mesh-group M. R MUST NOT
	other members of mesh-group M.		forward the SA message to other members of mesh-group M.
	(ii). If a member R of a mesh-group M receives an SA message from an		(ii). If a member R of a mesh-group M receives an SA message
	MSDP peer that is not a member of mesh-group M, and the SA		from an MSDP peer that is not a member of mesh-group M,
	message passes the peer-RPF check, then R forwards the SA		and the SA message passes the peer-RPF check, then R
	message to all members of mesh-group M and to any other		forwards the SA message to all members of mesh-group M
	msdp peers.		and to any other msdp peers.
	11. MSDP Connection State Machine		11. MSDP Connection State Machine
	MSDP uses TCP as its transport protocol. In a peering relationship,		MSDP uses TCP as its transport protocol. In a peering relationship,
	one MSDP peer listens for new TCP connections on the well-known port		one MSDP peer listens for new TCP connections on the well-known port
	639. The other side makes an active connect to this port. The peer		639. The other side makes an active connect to this port. The peer
	with the higher IP address will listen. This connection establishment		with the higher IP address will listen. This connection establishment
	algorithm avoids call collision. Therefore, there is no need for a		algorithm avoids call collision. Therefore, there is no need for a
	call collision procedure. It should be noted, however, that the		call collision procedure. It should be noted, however, that the
	disadvantage of this approach is that the startup time depends		disadvantage of this approach is that the startup time depends
	completely upon the active side and its connect retry timer; the		completely upon the active side and its connect retry timer; the
	passive side cannot cause the connection to be established.		passive side cannot cause the connection to be established.
	An MSDP peer starts in the DISABLED state. MSDP peers establish		An MSDP peer starts in the DISABLED state. MSDP peers establish
	peering sessions according to the following state machine:		peering sessions according to the following state machine:
	--------------->+----------+		--------------->+----------+
	/ | DISABLED |<----------		/ | DISABLED |<----------
	| ------>+----------+ \		| ------>+----------+ \
	| / |E1->A1 |		| / |E1->A1 |
	| | | |		| | | |
	| | V |E7->A7		| | V |E7->A7
	| | +----------+ E3->A3 +--------+		| | +----------+ E3->A3 +--------+
	| | | INACTIVE |------->| LISTEN |		| | | INACTIVE |------->| LISTEN |
	| | +----------+ +--------+		| | +----------+ +--------+
	| | E2->A2| ^ |E5->A5		| | E2->A2| ^ |E5->A5
	| | | | |		| | | | |
	| |E7->A6 V |E6 |		| |E7->A6 V |E6 |
	| \ +------------+ |		| \ +------------+ |
	| ------| CONNECTING | |		| ------| CONNECTING | |
	| +------------+ |		| +------------+ |
	E7->A8 | |E4->A4 |		E7->A8 | |E4->A4 |
	E8->A8 | | |		E8->A8 | | |
	E9->A8 | V |		E9->A8 | V |
	\ +-------------+ /		\ +-------------+ /
	--------------| ESTABLISHED |<---------		--------------| ESTABLISHED |<---------
	+-------------+		+-------------+
	| ^		| ^
	| |		| |
	E10->A9\______/		E10->A9 \______/
	11.1. Events
	E1) Enable MSDP peering with P		11.1. Events
	E2) Own IP address < P's IP address
	E3) Own IP address > P's IP address
	E4) TCP established (active side)
	E5) TCP established (passive side)
	E6) ConnectRetry timer expired
	E7) Disable MSDP peering with P
	(e.g. when one's own address is changed)
	E8) Hold Timer expired
	E9) MSDP TLV format error detected
	E10) Any other error detected
	11.2. Actions		E1) Enable MSDP peering with P
			E2) Own IP address < P's IP address
			E3) Own IP address > P's IP address
			E4) TCP established (active side)
			E5) TCP established (passive side)
			E6) ConnectRetry timer expired
			E7) Disable MSDP peering with P (e.g. when one's own address is
			changed)
			E8) Hold Timer expired
			E9) MSDP TLV format error detected
			E10) Any other error detected
	A1) Allocate resources for peering with P		11.2. Actions
	Compare one's own and peer's IP addresses
	A2) TCP active OPEN
	Set ConnectRetry timer to [ConnectRetry-Period]
	A3) TCP passive OPEN (listen)
	A4) Delete ConnectRetry timer
	Send KeepAlive TLV
	Set KeepAlive timer to [KeepAlive-Period]
	Set Hold Timer to [HoldTime-Period]
	A5) Send KeepAlive TLV
	Set KeepAlive timer to [KeepAlive-Period]
	Set Hold Timer to [HoldTime-Period]
	A6) Abort TCP active OPEN attempt
	Release resources allocated for peering with P
	A7) Abort TCP passive OPEN attempt
	Release resources allocated for peering with P
	A8) Close the TCP connection
	Release resources allocated for peering with P
	A9) Drop the packet
	11.3. Peer-specific Events		A1) Allocate resources for peering with P Compare one's own and
			peer's IP addresses
			A2) TCP active OPEN Set ConnectRetry timer to
			[ConnectRetry-Period]
			A3) TCP passive OPEN (listen)
			A4) Delete ConnectRetry timer Send KeepAlive TLV
			Set KeepAlive timer to [KeepAlive-Period]
			Set Hold Timer to [HoldTime-Period]
			A5) Send KeepAlive TLV
			Set KeepAlive timer to [KeepAlive-Period]
			Set Hold Timer to [HoldTime-Period]
			A6) Abort TCP active OPEN attempt
			Release resources allocated for peering with P
			A7) Abort TCP passive OPEN attempt
			Release resources allocated for peering with P
			A8) Close the TCP connection
			Release resources allocated for peering with P
			A9) Drop the packet
			11.3. Peer-specific Events
	The following peer-specific events can occur in the ESTABLISHED		The following peer-specific events can occur in the ESTABLISHED
	state, they do not cause a state transition. Appropriate actions are		state, they do not cause a state transition. Appropriate actions are
	listed for each event.		listed for each event.
	*) KeepAlive timer expired:		*) KeepAlive timer expired:
	-> Send KeepAlive TLV		-> Send KeepAlive TLV
	-> Set KeepAlive timer to [KeepAlive-Period]		-> Set KeepAlive timer to [KeepAlive-Period]
	*) KeepAlive TLV received:		*) KeepAlive TLV received:
	-> Set Hold Timer to [HoldTime-Period]		-> Set Hold Timer to [HoldTime-Period]
	*) Source-Active TLV received:		*) Source-Active TLV received:
	-> Set Hold Timer to [HoldTime-Period]		-> Set Hold Timer to [HoldTime-Period]
	-> Run Peer-RPF Forwarding algorithm		-> Run Peer-RPF Forwarding algorithm
	-> Set KeepAlive timer to [KeepAlive-Period] for those peers		-> Set KeepAlive timer to [KeepAlive-Period] for those peers
	the Source-Active TLV is forwarded to		the Source-Active TLV is forwarded to
	-> Send information to PIM-SM		-> Send information to PIM-SM
	-> Store information in cache		-> Store information in cache
	11.4. Peer-independent Events		11.4. Peer-independent Events
	There are also a number of events that affect more than one peering		There are also a number of events that affect more than one peering
	session, but still require actions to be performed on a per-peer		session, but still require actions to be performed on a per-peer
	basis.		basis.
	*) SA-Advertisement-Timer expired:		*) SA-Advertisement-Timer expired:
	-> Start periodic transmission of Source-Active TLV(s)		-> Start periodic transmission of Source-Active TLV(s)
	-> Set KeepAlive timer to [KeepAlive-Period] each time a		-> Set KeepAlive timer to [KeepAlive-Period] each time a
	Source-Active TLV is sent		Source-Active TLV is sent
	*) MSDP learns of a new active internal source (e.g. PIM-SM		*) MSDP learns of a new active internal source (e.g. PIM-SM
	register received for a new source):		register received for a new source):
	-> Send Source-Active TLV		-> Send Source-Active TLV
	-> Set KeepAlive timer to [KeepAlive-Period]		-> Set KeepAlive timer to [KeepAlive-Period]
	*) SG-State-Timer expired (one timer per cache entry):		*) SG-State-Timer expired (one timer per cache entry):
	-> Implementation specific, typically mark the cache entry for		-> Implementation specific, typically mark the cache entry
	deletion		for deletion
	12. Packet Formats		12. Packet Formats
	MSDP messages will be encoded in TLV format. If an implementation		MSDP messages are encoded in TLV format. If an implementation
	receives a TLV that has length that is longer than expected, the TLV		receives a TLV that has length that is longer than expected, the TLV
	SHOULD be accepted. Any additional data SHOULD be ignored and the		SHOULD be accepted. Any additional data SHOULD be ignored and the
	MSDP session should not be reset.		MSDP session should not be reset.
	12.1. MSDP TLV format:		12.1. MSDP TLV format
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length | Value .... |		| Type | Length | Value .... |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Type (8 bits)		Type (8 bits)
	Describes the format of the Value field.		Describes the format of the Value field.
	Length (16 bits)		Length (16 bits)
	Length of Type, Length, and Value fields in octets.		Length of Type, Length, and Value fields in octets.
	Minimum length required is 4 octets, except for		Minimum length required is 4 octets, except for
	Keepalive messages. The maximum TLV length is 9192.		Keepalive messages. The maximum TLV length is 9192.
	Value (variable length)		Value (variable length)
	Format is based on the Type value. See below. The length of		Format is based on the Type value. See below. The length of
	the value field is Length field minus 3. All reserved fields		the value field is Length field minus 3. All reserved fields
	in the Value field MUST be transmitted as zeros and ignored on		in the Value field MUST be transmitted as zeros and ignored on
	receipt.		receipt.
	12.2. Defined TLVs		12.2. Defined TLVs
	The following TLV Types are defined:		The following TLV Types are defined:
	Code Type		Code Type
	===========================================================		===================================================
	1 IPv4 Source-Active		1 IPv4 Source-Active
	2 IPv4 Source-Active Request		2 IPv4 Source-Active Request
	3 IPv4 Source-Active Response		3 IPv4 Source-Active Response
	4 KeepAlive		4 KeepAlive
	5 Reserved (Previously: Notification)		5 Reserved (Previously: Notification)
	Each TLV is described below.		Each TLV is described below.
	In addition, the following TLV Types are assigned but not described		In addition, the following TLV Types are assigned but not described
	in this memo:		in this memo:
	Code Type		Code Type
	===========================================================		====================================================
	6 MSDP traceroute in progress		6 MSDP traceroute in progress
	7 MSDP traceroute reply		7 MSDP traceroute reply
	12.2.1. IPv4 Source-Active TLV		12.2.1. IPv4 Source-Active TLV
	The maximum size SA message that can be sent is 9192 octets. The 9192		The maximum size SA message that can be sent is 9192 octets. The 9192
	octet size does not include the TCP, IP, layer-2 headers.		octet size does not include the TCP, IP, layer-2 headers.
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| 1 | x + y | Entry Count |		| 1 | x + y | Entry Count |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| RP Address |		| RP Address |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Reserved | Sprefix Len | \		| Reserved | Sprefix Len | \
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \
	| Group Address | ) z		| Group Address | ) z
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
	| Source Address | /		| Source Address | /
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Type		Type
	IPv4 Source-Active TLV is type 1.		IPv4 Source-Active TLV is type 1.
	Length x		Length x
	Is the length of the control information in the message. x is		Is the length of the control information in the message. x is
	8 octets (for the first two 32-bit quantities) plus 12 times		8 octets (for the first two 32-bit quantities) plus 12 times
	Entry Count octets.		Entry Count octets.
	Length y		Length y
	If 0, then there is no data encapsulated. Otherwise an IPv4		If 0, then there is no data encapsulated. Otherwise an IPv4
	packet follows and y is the value of the total length field		packet follows and y is the value of the total length field
	in the header of the encapsulated IP packet. If there are		in the header of the encapsulated IP packet. If there are
	multiple (S,G) entries in an SA message, only the last entry		multiple (S,G) entries in an SA message, only the last entry
	may have encapsulated data and it must reflect the source and		may have encapsulated data and it must reflect the source and
	destination addresses in the header of the encapsulated IP		destination addresses in the header of the encapsulated IP
	packet.		packet.
	Entry Count		Entry Count
	Is the count of z entries (note above) which follow the RP		Is the count of z entries (note above) which follow the RP
	address field. This is so multiple (S,G)s from the same domain		address field. This is so multiple (S,G)s from the same domain
	can be encoded efficiently for the same RP address. An		can be encoded efficiently for the same RP address. An
	SA message containing encapsulated data typically has an		SA message containing encapsulated data typically has an
	entry count of 1 (i.e. only contains a single entry, for		entry count of 1 (i.e. only contains a single entry, for
	the (S,G) representing the encapsulated packet).		the (S,G) representing the encapsulated packet).
	RP Address		RP Address
	The address of the RP in the domain the source has become		The address of the RP in the domain the source has become
	active in.		active in.
	Reserved		Reserved
	The Reserved field MUST be transmitted as zeros and MUST be		The Reserved field MUST be transmitted as zeros and MUST be
	ignored by a receiver.		ignored by a receiver.
	Sprefix Len		Sprefix Len
	The route prefix length associated with source address.		The route prefix length associated with source address.
	This field MUST be transmitted as 32 (/32).		This field MUST be transmitted as 32 (/32).
	Group Address		Group Address
	The group address the active source has sent data to.		The group address the active source has sent data to.
	Source Address		Source Address
	The IP address of the active source.		The IP address of the active source.
	Multiple (S,G) entries MAY appear in the same SA and can be batched		Multiple (S,G) entries MAY appear in the same SA and can be batched
	for efficiency at the expense of data latency. This would typically		for efficiency at the expense of data latency. This would typically
	occur on intermediate forwarding of SA messages.		occur on intermediate forwarding of SA messages.
	12.2.2. KeepAlive TLV		12.2.2. KeepAlive TLV
	A KeepAlive TLV is sent to an MSDP peer if and only if there were no		A KeepAlive TLV is sent to an MSDP peer if and only if there were no
	MSDP messages sent to the peer within [KeepAlive-Period] seconds.		MSDP messages sent to the peer within [KeepAlive-Period] seconds.
	This message is necessary to keep the MSDP connection alive.		This message is necessary to keep the MSDP connection alive.
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| 4 | 3 |		| 4 | 3 |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The length of the message is 3 octets which encompasses the one octet		The length of the message is 3 octets which encompasses the one octet
	Type field and the two octet Length field.		Type field and the two octet Length field.
	13. MSDP Error Handling		13. MSDP Error Handling
	If an MSDP message is received with a TLV format error, the session		If an MSDP message is received with a TLV format error, the session
	SHOULD be reset with that peer. MSDP messages with other errors, such		SHOULD be reset with that peer. MSDP messages with other errors, such
	as unrecognized type code, received from MSDP peers, SHOULD be silently		as unrecognized type code, received from MSDP peers, SHOULD be
	discarded and the session SHOULD not be reset.		silently discarded and the session SHOULD not be reset.
	14. SA Data Encapsulation		14. SA Data Encapsulation
	As discussed earlier, TCP encapsulation of data in SA messages MAY be		As discussed earlier, TCP encapsulation of data in SA messages MAY be
	supported for backwards compatibility with legacy MSDP peers.		supported for backwards compatibility with legacy MSDP peers.
	15. Security Considerations		15. Applicability Statement
	An MSDP implementation MAY use IPsec [RFC2401] or MD5 to secure control		MSDP is used primarily in two deployment scenarios:
	messages. In particular, the TCP connection between MSDP peers MAY
	be secured using IPsec or MD5. Implementations MUST be capable of
	working with peers which do not provide IPsec or MD5 security.
	16. Acknowledgments		15.1. Between PIM Domains
			MSDP can be used between PIM domains to convey information about
			active sources available in other domains. MSDP peering used in such
			cases is generally one to one peering, and utilizes the deterministic
			peer-RPF rules described in this spec (i.e., does not use mesh-
			groups). Peerings can be aggregated on a single MSDP peer, typically
			from one to hundreds of peerings, similar in scale, although not
			necessarily consistent, with BGP peerings.
			15.2. Between Anycast-RPs
			MSDP is also used between Anycast-RPs [RFC3446] within a PIM domain
			to synchronize information about the active sources being served by
			each Anycast-RP peer (by virtue of IGP reachability). MSDP peering
			used in this scenario is typically based on MSDP mesh groups, where
			anywhere from two to tens of peers can comprise a given mesh group,
			although more than ten is not typical. One or more of these mesh-
			group peers may then also have additional one-to-one peering with
			msdp peers outside that PIM domain as described in scenario A, for
			discovery of external sources. MSDP for anycast-RP without external
			MSDP peering is a valid deployment option and common.
			16. Intellectual Property
			The IETF takes no position regarding the validity or scope of any
			intellectual property or other rights that might be claimed to
			pertain to the implementation or use of the technology described in
			this document or the extent to which any license under such rights
			might or might not be available; neither does it represent that it
			has made any effort to identify any such rights. Information on the
			IETF's procedures with respect to rights in standards-track and
			standards-related documentation can be found in BCP-11. Copies of
			claims of rights made available for publication and any assurances of
			licenses to be made available, or the result of an attempt made to
			obtain a general license or permission for the use of such
			proprietary rights by implementors or users of this specification can
			be obtained from the IETF Secretariat.
			The IETF invites any interested party to bring to its attention any
			copyrights, patents or patent applications, or other proprietary
			rights which may cover technology that may be required to practice
			this standard. Please address the information to the IETF Executive
			Director.
			17. Acknowledgments
	The editors would like to thank the original authors, Dino Farinacci,		The editors would like to thank the original authors, Dino Farinacci,
	Yakov Rehkter, Peter Lothberg, Hank Kilmer, and Jermey Hall for their		Yakov Rehkter, Peter Lothberg, Hank Kilmer, and Jermey Hall for their
	orginal contribution to the MSDP specification. In addition, Bill		original contribution to the MSDP specification. In addition, Bill
	Nickless, John Meylor, Liming Wei, Manoj Leelanivas, Mark Turner,		Nickless, John Meylor, Liming Wei, Manoj Leelanivas, Mark Turner,
	John Zwiebel, Cristina Radulescu-Banu, Brian Edwards, Selina		John Zwiebel, Cristina Radulescu-Banu, Brian Edwards, Selina
	Priestley, IJsbrand Wijnands, Tom Pusateri, Kristofer Warell, Henning		Priestley, IJsbrand Wijnands, Tom Pusateri, Kristofer Warell, Henning
	Eriksson, Thomas Eriksson, Dave Thaler, and Ravi Shekhar provided		Eriksson, Thomas Eriksson, Dave Thaler, and Ravi Shekhar provided
	useful and productive design feedback and comments. Mike McBride,		useful and productive design feedback and comments. Mike McBride,
	Leonard Giuliano, Swapna Yelamanchi, Toerless Eckert and Ishan Wu		Leonard Giuliano, Swapna Yelamanchi, Toerless Eckert, John Meylor and
	contributed to the final version of the draft.		Ishan Wu contributed to the final version of the draft.
	17. Editors' Address:		18. Security Considerations
	David Meyer		An MSDP implementation MAY use IPsec [RFC2401] or MD5 to secure
	Email: dmm@maoz.com		control messages. In particular, the TCP connection between MSDP
			peers MAY be secured using IPsec or MD5. Implementations MUST be
			capable of working with peers which do not provide IPsec or MD5
			security. SA Filters and limits should always be used with MSDP to
			limit the sources and groups that will be passed between RPs. For
			example, MSDP SA messages announcing the following (S,G) ranges that
			SHOULD NOT be globally routed:
	Bill Fenner		(*,224.0.1.2/32) SGI-Dogfight
	AT&T Labs -- Research		(*,224.0.1.3/32) Rwhod
	75 Willow Road		(*,224.0.1.22/32) SVRLOC
	Menlo Park, CA 94025		(*,224.0.1.22/32) Microsoft-DS
	Email: fenner@research.att.com		(*,224.0.1.35/32) SVRLOC-DA
			(*,224.0.1.39/32) CISCO-RP-ANNOUNCE
			(*,224.0.1.40/32) CISCO-RP-DISCOVERY
			(*,224.0.2.2/32) SUN-RPC
			(*,224.77.0.0/16) Norton Ghost
			(*,224.128.0.0/24) Control plane of IGMP snoopers
			(*,225.0.0.0/24) Control plane of IGMP snoopers
			(*,225.1.2.3/32) Altiris
			(*,225.128.0.0/24) Control plane of IGMP snoopers
			(*,226.0.0.0/24) Control plane of IGMP snoopers
			(*,226.77.0.0/16) Norton Ghost
			(*,226.128.0.0/24) Control plane of IGMP snoopers
			(*,227.0.0.0/24) Control plane of IGMP snoopers
			(*,227.128.0.0/24) Control plane of IGMP snoopers
			(*,228.0.0.0/24) Control plane of IGMP snoopers
			(*,228.128.0.0/24) Control plane of IGMP snoopers
			(*,229.0.0.0/24) Control plane of IGMP snoopers
			(*,229.128.0.0/24) Control plane of IGMP snoopers
			(*,230.0.0.0/24) Control plane of IGMP snoopers
			(*,230.128.0.0/24) Control plane of IGMP snoopers
			(*,231.0.0.0/24) Control plane of IGMP snoopers
			(*,231.128.0.0/24) Control plane of IGMP snoopers
			(*,232.0.0.0/24) Control plane of IGMP snoopers
			(*,232.128.0.0/24) Control plane of IGMP snoopers
			(*,233.0.0.0/8) Source-Specific Multicast
			(*,233.0.0.0/24) Control plane of IGMP snoopers
			(*,233.128.0.0/24) Control plane of IGMP snoopers
			(*,234.0.0.0/24) Control plane of IGMP snoopers
			(*,234.42.42.42/32) Phoenix/StorageSoft ImageCast
			(*,234.128.0.0/24) Control plane of IGMP snoopers
			(*,234.142.142.42/31) Phoenix/StorageSoft ImageCast
			(*,234.142.142.44/30) Phoenix/StorageSoft ImageCast
			(*,234.142.142.48/28) Phoenix/StorageSoft ImageCast
			(*,234.142.142.64/26) Phoenix/StorageSoft ImageCast
			(*,234.142.142.128/29) Phoenix/StorageSoft ImageCast
			(*,234.142.142.136/30) Phoenix/StorageSoft ImageCast
			(*,234.142.142.140/31) Phoenix/StorageSoft ImageCast
			(*,234.142.142.142/32) Phoenix/StorageSoft ImageCast
			(*,235.0.0.0/24) Control plane of IGMP snoopers
			(*,235.128.0.0/24) Control plane of IGMP snoopers
			(*,236.0.0.0/24) Control plane of IGMP snoopers
			(*,236.128.0.0/24) Control plane of IGMP snoopers
			(*,237.0.0.0/24) Control plane of IGMP snoopers
			(*,237.128.0.0/24) Control plane of IGMP snoopers
			(*,238.0.0.0/24) Control plane of IGMP snoopers
			(*,238.128.0.0/24) Control plane of IGMP snoopers
			(*,239.0.0.0/8) Administratively Scoped Groups
			(*,239.0.0.0/24) Control plane of IGMP snoopers
			(*,239.128.0.0/24) Control plane of IGMP snoopers
	18. REFERENCES		19. IANA Considerations
	[IANA] http://www.iana.org		This document defines seven MSDP TLV values. Values for new MSDP TLV
			types are to be allocated using an IESG Approval or Standards Action
			processes. The policy for assigning new MSDP TLV values SHOULD BE
			defined in the document defining the new TLV values.
	[RFC768] Postel, J. "User Datagram Protocol", RFC 768, August,		20. References
	1980.
	[RFC1191] Mogul, J., and S. Deering, "Path MTU Discovery",		20.1. Normative References
	RFC 1191, November 1990.
	[RFC1771] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4		[RFC1142] Oran, D. "OSI IS-IS Intra-domain Routing
	(BGP-4)", RFC 1771, March 1995.		Protocol", RFC 1142, February 1990.
	[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate		[RFC2178] Moy, J., "OSPF Version 2", RFC 2178, April, 1998.
	Requirement Levels", RFC 2119, March, 1997.
	[RFC2283] Bates, T., Chandra, R., Katz, D., and Y. Rekhter.,		[RFC2283] Bates, T., Chandra, R., Katz, D., and
	"Multiprotocol Extensions for BGP-4", RFC 2283,		Y. Rekhter., "Multiprotocol Extensions for
	February 1998.		BGP-4", RFC 2283, February 1998.
	[RFC2362] Estrin D., et al., "Protocol Independent Multicast -		[RFC2362] Estrin D., et al., "Protocol Independent
	Sparse Mode (PIM-SM): Protocol Specification", RFC		Multicast - Sparse Mode (PIM-SM): Protocol
	2362, June 1998.		Specification", RFC 2362, June 1998.
	[RFC2365] Meyer, D. "Administratively Scoped IP Multicast", RFC		[RFC2365] Meyer, D. "Administratively Scoped IP Multicast",
	2365, July, 1998.		RFC 2365, July, 1998.
	[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for		[RFC2401] Kent, S. and R. Atkinson, "Security Architecture
	the Internet Protocol", RFC 2401, November 1998.		for the Internet Protocol", RFC 2401, November 1998.
	[RFC2784] Farinacci, D., et al., "Generic Routing Encapsulation		[RFC3446] Kim, D., et al., "Anycast Rendezvous Point (RP)
	(GRE)", RFC 2784, March 2000.		Mechanism using Protocol Independent Multicast
			(PIM) and Multicast Source Discovery Protocol
			(MSDP)", RFC 3446, January, 2003.
	19. Full Copyright Statement		20.2. Informative References
	Copyright (C) The Internet Society (2003). All Rights Reserved.		[RFC2119] S. Bradner, "Key words for use in RFCs to
			Indicate Requirement Levels", RFC 2119, March,
			1997.
			21. Editor's Addresses
			Bill Fenner
			AT&T Labs -- Research
			75 Willow Road
			Menlo Park, CA 94025
			Email: fenner@research.att.com
			David Meyer
			Email: dmm@maoz.com
			22. Full Copyright Statement
			Copyright (C) The Internet Society (2003). All Rights Reserved.
	This document and translations of it may be copied and furnished to		This document and translations of it may be copied and furnished to
	others, and derivative works that comment on or otherwise explain it		others, and derivative works that comment on or otherwise explain it
	or assist in its implementation may be prepared, copied, published		or assist in its implementation may be prepared, copied, published
	and distributed, in whole or in part, without restriction of any		and distributed, in whole or in part, without restriction of any
	kind, provided that the above copyright notice and this paragraph are		kind, provided that the above copyright notice and this paragraph are
	included on all such copies and derivative works. However, this		included on all such copies and derivative works. However, this
	document itself may not be modified in any way, such as by removing		document itself may not be modified in any way, such as by removing
	the copyright notice or references to the Internet Society or other		the copyright notice or references to the Internet Society or other
	Internet organizations, except as needed for the purpose of		Internet organizations, except as needed for the purpose of
	developing Internet standards in which case the procedures for		developing Internet standards in which case the procedures for
	copyrights defined in the Internet Standards process must be		copyrights defined in the Internet Standards process must be
	followed, or as required to translate it into languages other than		followed, or as required to translate it into languages other than
	English.		English.
	The limited permissions granted above are perpetual and will not be		The limited permissions granted above are perpetual and will not be
	revoked by the Internet Society or its successors or assigns.		revoked by the Internet Society or its successors or assigns.
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